1. Field Of The Invention
This invention relates to offset lithographic printing presses having a spray rail and series of spray nozzles for supplying fluid to the press during printing operations. More particularly, the invention relates to a fluid stop module that acts in cooperation with the spray rail to provide a shield that enables control of the area of coverage achieved by fluid exiting the spray nozzles such that the area of coverage corresponds to the width of the web of material being utilized in the printing press.
2. Description Of Prior Art
Lithography is the art or process of printing from a flat stone or metal plate. Lithography is distinguished from other forms of printing, in part, by the absence of the use of relief to distinguish between the areas to be printed and those to be left blank. The lithographic method is based upon the repulsion between immiscible liquids, such as oil-based inks, and water. The process begins by the etching of a design on a surface. A grease-like material that is attracted to the etched area is then applied to the surface and takes the form of the design. Water is then added to the surface. The greased areas repel the water which ensures that only the ungreased areas become water saturated. The printing ink subsequently applied will then be repelled by the ungreased water-saturated areas and absorbed by the greased areas. This creates the design in ink for transfer to a web.
To encourage an even coating of water for printing, water is generally introduced to a dampener roller and subsequently transferred to the printing plate. Various methods for applying water to a dampener have been utilized in offset lithographic presses. One method typically utilizes a spray rail which comprises a series of spray nozzles that direct water onto the dampener.
In order to properly saturate the dampener for adequate transfer of water to the printing plate, spray nozzles must span the width of the dampener. It is important that water is transferred to the printing plate over a large enough area to span the largest width web the printing press can handle. As a consequence, with fixed spray rails, when smaller widths of web are being utilized in printing, excess water is applied to the dampener and transferred to the press beyond the limits of the web. The excess water is not absorbed and has a tendency to flood the machinery.
As water is corrosive to some components of a printing press, this excess water can lead to premature corrosion, especially to the outer edges of the press and other exposed areas resulting in a significant reduction in the useful life of the press. As well as being detrimental to the machinery, excess water is also expelled from the press soaking press operators and other workers in the vicinity. Excess water is also deposited on the floor where it might precipitate an accident.
To reduce both corrosion of the press and danger to the workers, it is desirable to minimize the exposure of the press to excess water during operation. It is consequently desirable to be able to adjust the coverage area of fluid exiting the spray nozzles to provide a water film on the printing plate that corresponds to the width of the web of material being utilized in the printing press.
The fluid stop device of this invention achieves such a result. Regulation of the movement of a shield that blocks the flow of fluid from the spray nozzles allows adjustment of the width of the dampener moistened by fluid from a spray bar. A dial situated on top of the water stop module allows the operator to select the width limit of the spray to match the width of web on the press and thereby minimize the excess water in the press machinery.